High pressure hydraulic systems

Abstract

In a high pressure hydraulic system wherein a source supplies pressurized fluid to a slave unit through a control valve operative to maintain the slave unit in a desired condition, leakage from the slave unit past the control valve when the source is inoperative is prevented by a control valve comprising two solenoid-operated valves, oppositely acting and arranged in series between the source and the slave unit, each valve being closed to prevent flow through the valve in a direction towards the other valve and opened to permit flow in both directions, under the control of a solenoid and the pressure differential acting across the valve. A seating portion on the valve located between the other valve and the slave unit is of elastomeric material to provide a leakproof seal when that valve is closed. In the construction shown the slave unit is an hydraulic suspension strut, and the system is adapted as a vehicular suspension levelling system, with the valves and the source being manipulated as required by an electronic control system.

I claim: 
     
       1. A high pressure hydraulic system comprising a slave unit, a source of hydraulic fluid for supplying said slave unit with fluid under pressure, and a control valve assembly for controlling the supply of hydraulic fluid to said slave unit, said control valve assembly comprising first and second solenoid-operated valves, and first and second solenoids for respectively operating said first and second valves, a pressure differential acting across each of said valves also to operate said valves, said valves being oppositely acting and arranged in series with said first valve located between said source and said second valve, and said second valve located between said first valve and said slave unit, each one of said valves being movable into a closed position in which fluid flow through said one valve in a direction towards the other of said valves is substantially prevented, and an open position in which fluid flow through said one valve in both directions is permitted, said solenoids and said pressure differentials across said valves controlling movement of said valves between said open and said closed position, and each one of said valves comprising a seating member having a seating portion and a valve member having a complementary seating portion for engagement with said seating portion of said seating member, said seating portion of one of said members of said second valve comprising an element of elastomeric material to provide a substantially leakproof seal when said second valve is in said closed position. 
     
     
       2. A high pressure hydraulic system as claimed in claim 1, wherein said seating member of said second valve comprises an element of elastomeric material. 
     
     
       3. A high pressure hydraulic system as claimed in claim 1, wherein each one of said valves acts as a one-way valve when in said closed position, permitting fluid flow in a direction from the other of said valves. 
     
     
       4. A high pressure hydraulic system as claimed in claim 3, wherein each one of said solenoids is energised in order to move the respective one of said valves into said open position only when said pressure differential acting across said valve against the action of said solenoid is insignificant. 
     
     
       5. A high pressure hydraulic system as claimed in claim 4, wherein continuous energisation of each one of said solenoids causes the respective one of said valves, when in said open position, to remain in said open position irrespective of the direction of fluid flow, said pressure differential acting across said valve to determine the position of said valve when said solenoid is de-energised. 
     
     
       6. A high pressure hydraulic system as claimed in claim 5, wherein said source is normally maintained at a low pressure, and when operative is cycled slowly and continuously over a range of pressures which includes, and exceeds the range of pressures which occur in said slave unit. 
     
     
       7. A high pressure hydraulic system as claimed in claim 6, wherein said solenoids are normally de-energised so that said second valve is held in said closed position by said pressure differential across said second valve and said first valve is in said open position, said source being operative to cycle said source pressure, said solenoid for said first valve being energised to hold said first valve in said open position whilst said source pressure rises, said second valve acting as a one-way valve when said source pressure exceeds the pressure in said slave unit to cause fluid to flow into said slave unit until either said source pressure falls below said slave pressure to close said second valve or said solenoid for said first valve is de-energised to close said first valve, said second valve closing and said first valve opening when said source pressure falls below said slave pressure. 
     
     
       8. A high pressure hydraulic system as claimed in claim 6, wherein said solenoids are normally de-energised so that said second valve is held in said closed position by said pressure differential across said second valve and said first valve is in said open position, said source being operative to cycle said source pressure, and said solenoid for said second valve being energised so as to cause said second valve to move into said open position when said pressure differential acting across said second valve is sufficiently reduced, said second valve being held in said open position whilst said solenoid is energised and said source pressure rises above said slave pressure so that fluid flows into said slave unit causing said first valve to close, and said first valve acting as a one-way valve to allow fluid to flow out of said slave unit when said source pressure falls below said slave pressure until said solenoid for said second valve is de-energised to close said second valve. 
     
     
       9. A high pressure hydraulic system as claimed in claim 5, wherein said source is normally maintained at a high pressure, and when operative is cycled slowly and continuously over a range of pressures which includes, and extends beyond, the range of pressures which occur in said slave unit, and said solenoids are normally de-energised so that said first valve is held in said closed position by said pressure differential across said first valve and said second valve is in said open position. 
     
     
       10. A high pressure hydraulic system as claimed in claim 1, wherein said seating portions of one of said members of said first valve also comprises an element of elastomeric material to provide a substantially leakproof seal when said first valve is in said closed position. 
     
     
       11. A high pressure hydraulic system as claimed in claim 1, further comprising an electronic control system for controlling energisation and de-energisation of said solenoids. 
     
     
       12. A high pressure hydraulic system as claimed in claim 11, wherein said electronic control system also controls operation of said source. 
     
     
       13. A high pressure hydraulic system as claimed in claim 1, wherein said slave unit comprises an hydraulic suspension strut for a wheel of a vehicle. 
     
     
       14. A high pressure hydraulic system as claimed in claim 13, wherein said suspension strut produces ride height signals according to the loading of said vehicle and incorporating an electronic control system for manipulating said control valve assembly and said source in response to said ride height signals to constitute a suspension levelling system. 
     
     
       15. A high pressure hydraulic system as claimed in claim 14, wherein said source comprises a manifold for supplying at least two hydraulic suspension struts simultaneously.